Amplification and rectification means for use in a photographic exposure timer



Apnl 3, 1962 J. R. BATINA ET AL AMPLIFICATION AND RECTIF'ICATION MEANSFOR USE IN A PHOTOGRAPHIC EXPOSURE TIMER Original Filed Oct. 5, 1954 RIFM .L ans. .L

FEE @958 w INVENTORQ. Jerome 554222120. lemzeafzflf Grows, WM M PatentedApr. 3, 1962 3,028,561 AMPLIFEQATEQN AND RECTKFHCATIQN MEANS FER USE lNA PHOTOGRAPHEC EXPOSURE Til ERR Jerome R. Batina and Kenneth E. Grosse,Chicago, Ill., assignors to W. M. Welch Manufacturing Company, Chicago,Ill., a corporation of Illinois Griginal application Get. 5, 1954, Ser.No. 460,454, now Patent No. 2,885,563, dated May 5, 1959. Divided andthis application Dec. 2, 1957, Ser. No. 7%,235

3 Claims. (ill. 329-492) The present invention relates to an improvedtiming system which is particularly devised for use in determining andcontrolling exposure periods in the printing of films such as aphotographic negative. The timing system includes an improved component,in the form of an adjustably biased rectifier unit which is also suitedfor use generally where rectification is required. This application is adivision of our copending application, Serial No. 460,454, filed October5, 1954, and which is a continuation-in-part of our copendingapplication, Serial No. 394,687, filed November 27, 1953, now abandoned.

The timing system operates on the general principle that a photoelectricelement will originate and forward an electric signal proportional inintensity to a radiant flux to which it is subjected. If this signal isamplified and applied to an interpretive and integrative unit which willtransform the signal into an output voltage expressive of a timeinterval, the output voltage can be used to control energization andde-energization of a light source from which the radiant flux impingingthe photoelectric element was derived. In further accordance with theinvention, the integrative unit produces an output voltage which risesin value at a linear rate with reference to the value of its appliedvoltage. Hence, since the applied voltage is directly proportional tothe intensity of the original light flux at the photoelectric element,i.e., inversely proportional to the density of a film or negativeexposed, it is seen that the duration of rise of the output voltagerepresents a time interval which is inversely proportional to the amountof light flux impinging the phototube. Such voltage is accordingly usedby an appropriate control or trigger unit to de-energize the exposurelight source after an exposure interval so determined by the integrator.A dense negative is thus exposed a longer time, a less dense a shortertime, and, in the main, a proper exposure will be had of negatives ofaverage to less than average density.

However, for perfect results the linear timing response of theintegrator will require some compensation or correction in the case ofvery dense negatives, due to failure in reciprocity of the photographicpaper, and the same may be true in the case of extremely lightnegatives.

Other adaptations of the timing and control system will suggestthemselves to those skilled in the art, however its embodiment in anautomatic photographic exposure timer is an ideally illustrative one.The requirements of such a system are exacting. It should eliminate thehuman factor as much as possible, and be capable of being operated witha minimum of control or adjusting manipulations. It should copesuccessfully with the problem of satisfactorily exposing a wide varietyof photographic negatives which are the work of amateurs as well asprofessional photographers. It must operate satisfactorily on a fullrange of negatives, including those of average contrast and density,those having a predominantly light colored background and dark subject,and vice versa, and all intermediate states. The system should beversatile as regards the exposure requirements of different photographicpapers.

As a factor with which the present invention does not deal in detail,whatever may be the type of optical-photoelectric unit used inassociation with the system it must faithfully reproduce a projectedimage in reference to the intensity of the electric current which itforwards, and in this connection the system should embody an adjustmentfor a change in enlarger magnification. It should be at least ninetyseven percent efiicient at any magnification or negative density, sothat the amount of rework on the prints will not exceed three percent.It should operate so that the majority of exposures are less than onesecond.

Generally considered, the improved timer as embodied in a photographicexposure system having these requirements comprises a source of lightfor exposure of a photographic film or negative, such as a conventionalenlarger; a photoelectric unit, preferably capable of forwarding analternatingly modulated signal when exposed to an image of the negative,since it is desirable to build up the photoelectric signal in an A.-C.amplifier; an interpretive or translative unit in the form of anintegrating amplifier to which the amplified signal is fed after beingrectified and converted to steady D.-C. form, and which faithfullyproduces a timing signal at its output which rises at a rate bearing alinear relation to the converted signal; and a control or trigger unitoperated by the integrator which applies to the exposure light source acontrol action, translated in terms of time from the integrators appliedvoltage.

Reference has been made to a possible failure of material in theexposure phase, in respect to non-reciprocity of printing paper, whichwill have a disturbing effect on the printing result if thephotoelectric signal is faithfully translated into terms of time to aunit which controls exposure. To overcome this the invention pro- Videsmeans operative in the rectification of the amplified photoelectricsignal to optionally compensate for the non-reciprocity referred to.

In explanation, it has been found that most photographic printingemulsions are not strictly linear in their relation of exposure time andexposure light throughout the entire range of their response to light,especially in the low range. Here the required exposure time for aperfect result is greater than would be expected were the responsivityof the paper a linear one. This being the case, it is desirable toafford means to compensate for the non-linearity by increasing theexposure time; otherwise the insufficient photoelectric signal will betranslated in linearly responsive fashion into an excessively rapidlyrising timing signal at the integrator output. The means for thispurpose as contemplated by the invention take the form of means foradjustably biasing a rectifier by which the amplified photoelectricsignal is converted, so that the integrator will then receive a D.-C.signal which it can in turn modify properly for use in the exposurecontrol operation. The adjustably biased rectifier unit is of itself anindependent part of the invention, since it is well suited to otherapplications.

As a further refinement in the timer, selection by range switching orvoltage divider is employed to lend versatility in respect to theexposure requirements of different negatives, as well as other variablefactors with which those skilled in the photographic art are familiar.

As indicated above, the integrating amplifier of the system is anelectronic unit Whose output voltage will rise at a linear rate inrelation to its applied or input voltage. This is due to the fact that apart of the output is reflected back to its input grid, i.e., indegenerative feed back, and the linearly rising output voltage is theproduct. The control or trigger unit is shown as a triode, to the gridof which this voltage is applied, and a normally closed switching relayacts when a predetermined potential level has been reached by theintegrator output to open the circuit of the exposure light source. Thisis preferably done through an imprvoed holding relay circuit whichautomatically restores the input side of the integrator to a normaluncharged condition upon each operation of the trigger, and keeps it inthat condition until the next exposure cycle takes place.

The timed rise of the integrating amplifier output, depending upon themagnitude of a direct current voltage applied thereto, which is in turninversely proportional to the light transmitted through a negative,permits the normally closed relay of the trigger unit to keep thecircuit of the exposure light source closed until the trigger tubepasses current. Thus for a higher impressed voltage, at the integratorgrid, due to a light negative, its output voltage will rise more rapidlyand the exposure time will be shorter. With a denser negative thetrigger tube and relay will act to hold the light source circuit closeda longer time. in either case the time interval may optionally be in alinear or non-linear relation to the density of the negative, asdetermined at the adjustable rectifier.

It will become more evident, as the description proceeds that, either asa component of or as an independent subcombination of the timer, theadjustably biased rectifier unit is a highly valuable improvement, forthe further reason that it alfords a means for controlling andcompensating undesirable contact potential in a rectifier tube, i.e.,between the electrodes thereof. This permits preamplification of an A.C.signal to a considerable degree, as by thermionic circuit, transformer,or both, and full wave rectification without the effect of contactpotential.

The invention provides a system which satisfies the operationalrequirements previously outlined, being capable of timing properly andsustainedly under a normal, single cycle operation or with automaticrecycling in association with an automatic paper advance mechanism. Itpermits the making of more than 600 exposures an hour. Yet anotheradvantage of the system is that it is composed of units which areindividually replaceable readily when necessary, thereby insuringagainst any sustained interruption of operation.

The foregoing statements are indicative in a general way of the natureof the invention. Other and more specific objects will be apparent tothose skilled in the art upon a full understanding of the compositionand operation of the system.

A single embodiment of the invention is presented herein for purpose ofillustration. It will be appreciated that the invention may beincorporated in other modified forms coming equally within the scope ofthe appended claims.

In the drawings:

FIG. 1 is a schematic layout illustrating optical and electricalcomponents of the improved system and the wiring of the latter;

FiG. 2 is a block diagram showing the essential operating components ina simpler fashion; and

FIG. 3 is a schematic wiring diagram of one of the components of thesystem of FIG. 1, in the form of a biased rectifier arrangement forlinearity compensation under certain conditions of operation, either inthe installation of FIG. 1 or for other purposes.

Considering first FIG. 2, a simplified layout, the improved system iscomposed of a suitable light source 10, such as a conventionalphotographic enlarger or other exposure device which transmits radiantenergy, under the control of other units of the system, through aphotographic negative or film 11 into impingement with the cathode of aphototube 12 of a photoelectric probe unit, generally designated 13.Thus a projected image of negative 11 originates and forwards a weakelectrical signal which is directly proportional in intensity to thetotal radiant flux impinging the phototube, i.e., inversely proportionalto the density of the negative.

Since a signal which is usable, in regard to sensitivity and stability,for the present purpose can best be built up in an alternating currentamplifier, the probe unit 13 is preferably a magnetically modulated one,as hereinafter described, in general accordance with the disclosure ofthe patent to Kalrnus et al., No. 2,605,428, dated July 29, 1952.

The anode of phototube 12 is connected to the input grid of AC.amplifier 14, the cathode side of which is appropriately grounded, andthe output of the amplifier is impressed on an improved type ofadjustable full wave rectifier and voltage doubler unit 15. Unit 15converts the amplified AC. potential to a steady one of negativepolarity at the input side of a subsequent translative unit 16, in theform of an integrating amplifier, which operates on direct current.

The rectifier output is preferably applied to integrator 16 through anappropriate voltage divider type of selector 17 (F1 1), by which thesystem may be appropriately adjusted in regard to integrator inputvoltage, as determined, for example, by the preliminary exposure andprinting of photographic test strips.

Integrator 16 acts in conjunction with photoelectric probe 13 toestablish a tirne-integral relationship with the radiant flux of aprojected image striking phototube 12, i.e., with the average density ofa photographic negative. Output voltage of the integrator, linearly ornon-linearly related in its rate of rise to the flux intensity, inaccordance with the setting of unit 15, is made effective by trigger orcontrol unit 18 to determine the duration of energization of lightsource 10, through the agency of a suitable holding and restorativecircuit, generally designated 19 and hereinafter described in detail.

Now considering in greater detail the component units of the improvedtimer and the operating connections thereof, light source 10 may be a1000 watt lamp of a conventional enlarger, energized by a volt A.C. line20. This is of course under the control of trigger device 18 andassociated holding circuit 19. Negative 11 is removably supported by thefilm holder of the enlarger, which projects an image of the negativeonto phototube 12, either directly or by reflection.

Suitable optical composing, focusing and phototube exposing provisionsmay be associated with photoelectric probe unit 13, for example of thetype illustrated and described in a copending application of Stanton H.Petry and Kenneth E. Grosse, Serial No. 423,960, filed April 19, 1954,now Patent 2,800,834, issued July 30, 1957, in which a projected imageis reflected to the probe device from a work surface on which thephotographic paper is supported. Alternatively, probe 13 may beenergized directly by light transmitted from an image.

As indicated above, the probe is preferably a magnetically modulatedone, phototube 12 being in the field of an electromagnet 22 whose coil23 is supplied through leads 24 with a 6 volt, 60 cycle potential. Alead 25 connects the anode of tube 12 to the input grid of a narrow bandor tuned alternating current amplifier 14, the cathode of the phototubebeing grounded in common with the rest of the cathode connections of theamplifier and other tubes as shown. Plus voltage of the amplifier, as ofthe remaining electronic tubes of the system, is through a lead 26supplied by a B battery plus terminal.

Rectification of the output voltage of amplifier 14, and the reasontherefor, have been referred to, the input terminal of adjustablerectifier unit 15 being supplied through a lead 27. The steady output ofthis unit is impressed on integrator 16 through lead 28 and selectorvoltage divider 17, by which it is adjusted as to value to compensatefor any of several variable photographic factors at enlarger 10 andprobe unit 13.

The input lead 27 to rectifier unit 15 is capacity coupled in anentirely conventional fashion to a standard amplifier tube 127 which hasits plate voltage supplied through the primary coil of a transformer 128connected to B voltage lead 26. This transformer further steps up theamplified A.C. output of tube 127 and applies it to the terminals of astandard bridge rectifier, generally designated 129. The result, asdescribed above, is a high voltage D.C. output at lead 28 to voltagedivider 17, the value of which voltage will reflect the intensity ofradiant flux at the light source in a linear ratio.

If perfect results are to be attained in the printing of commerciallyavailable papers throughout the entire range of densities of anynegative, it is highly desirable in printing dense negatives tocompensate the linearity of performance of the circuit thus fardescribed, for, as has been stated above, a greater exposure time isrequired in the range of low light flux impinging the printing paperthan would be indicated by a truly linear reciprocity curve for thepapers emulsion.

Accordingly, the invention provides a corrective D.C. biasing voltage ofopposite polarity, derived from a potentiometer 130 connected betweenthe B+ supply and ground, for application to rectifier 129.Potentiometer 130 is adjustably tapped, in the illustrated embodiment,to the cathode of the first tube of full wave rectifier 129, being soconnected for the particular purpose of the timing system. In anotherapplication the rectifier connections may be reversed.

The biasing connection described above permits a setting of unit 15, atits potentiometer 130, in which its output voltage may be in linear ornon-linear ratio to its input, in the latter case compensating for thevariation introduced by paper failure and the like. Moreover, this ispossible whether the disturbing phenomenon exists in the low or highrange of light flux impinging the paper, or both. A non-linear relationof the rectifier input in respect to time, as determined by integrator16, necessarily follows.

A further advantage of the adjustable biasing arrangement described,equally benefiting the illustrated adaptation as well as an adaptationin a different setting, resides in the fact that it aifords means tocontrol and olfset contact potential in the rectifier. This isparticularly desirable in an instance in which the AC. voltage to berectified has been considerably amplified as it is applied to the inputof the unit.

The amplified direct current voltage, inverted to negative polarity, issupplied to the input grid of the first tube 29 of integrator 16. Thisis a pentode whose operating voltages are derived from a voltage divider3t and the anode of tube 29 is connected to a triode 31, with adegenerative fced back hookup from the cathode of the latter through acapacitor 32 to the input grid of tube 2 9. Thus the integrator circuitprovides a rising voltage output, of time rate of rise linearly ornon-linearly proportional to input signal in accordance with the settingof linearity control potentiometer 130, by reflecting a part of theformer back to its input side.

There is also a grounded restorative or automatic recycling circuitassociated with the grid of integrator tube 29 through leads 34, 35 to apart of holding unit 19, for the purpose of discharging capacitor 32 andreturning the integrator to normal condition at the end of each timingcycle, particularly when automatic paper advance is employed. Thisinvolves a double pole, double throw relay in unit 19, schematicallyshown and generally designated 36. Relay 36 comprises a normally opencontact arm 37 and a normally closed contact arm 38, to the terminals ofwhich leads 34, 35 are connected, both arms being under the control ofrelay coil 39.

Contact arm 37 and coil 39 of relay 36 are in series and are also wired,respectively, to one terminal of the 110 volt line 29 and to a terminalcontactor 4d of a normally closed relay, generally designated 41, whosecoil is series connected in the output circuit of a triode 42 of thecontrol or trigger unit 18. The other contactor terminal is connected bylead 43 with the second terminal of line 20. 'The input grid of tube 42is supplied through a connection to the cathode of second integratortube 31, and plate voltage for the system is supplied from a B batterypositive connection to the plate of tube 42.

Trigger unit 18 of the system may include a multiple button range switchpanel 44 in the output circuit of tube 42. By this means cathode voltagemay be adjusted as desired to accommodate the system once and for allupon initial installation to the timing of film exposure, for example asmay be dictated by different vogues or regional tastes in differentparts of the country.

The present system may be used optionally for printing alone, eitherrepeated cycling or single exposure, or for preliminary composingwithout exposing the photographic paper, as in association with a probedevice accordingto the application of Petry and Grosse, identifiedabove. Accordingly, the circuit employs a normally open relay '45 whosecoil may be connected between lead 43 and the coil 39 of relay 36 bymeans of a manually adjustable selector arm 46 of a print-compose switch47. The contactor terminal of relay 45 is series connected with thefilament of enlarger lamp 10 in a line-supplied circuit which parallelsthat of holding unit 19. The contacts of switch 47 are connected to aninstantaneous switch 48, both in shunt relation to the contactor arm 37of relay 36, and switch '48 is the master actuating switch for thesystem for the timing cycle, as distinguished from the composing cycle.

In the operation of the improved timer system, let it first be assumedthat it is desired to compose prior to printing, with the assistance ofthe device of the Petry et al. application. In such case the phototube12 of probe unit 13 is shielded oil and the timer circuit isineffective. Arm 46 of print-compose switch 47 is positioned in thedotted line position of FIG. 1, and a circuit exists through relay 45 toclose its contactor and complete a circuit through illuminate lamp 10for composmg.

When it is desired to time an exposure and printing cycle the selectorarm of switch 47 is shifted to the solid line position, and p-hototube12 is exposed to view an image projected by the enlarger lamp 10 whenthe latter is lighted. Upon closing of instantaneous switch 48, acircuit is completed from one side of line 20 through the closedcontactor 40 of relay 41, through coil 39 of relay 36, and throughswitch 43 to the other side of the line. The coil of relay 45 is alsoenergized to complete the lamp circuit, and energization of coil 39 doestwo things: it complete-s a holding circuit through its contact arm 37and it opens its contact arm 38, thus opening the grounding circuit forthe grid of integrator tube 29 through leads 34, 35.

Timing ensues for a period which ends when the input voltage at tube 42has been brought by integrator 16 to a critical value sufficient tocause that tube to pass current, whereupon relay 4]. is energized toopen the holding circuit at contactor '40. De-energization of coil 39 ofrelay 36 opens its contact arm 37 and closes its contact arm 38, thusgrounding capacitor 32 and restoring integrator tube 29 to normalcondition, so that there will be no recommencement of timing operationin the event an unintended signal enters the system. De-energization ofrelay '45 of course breaks the lamp circuit.

We claim:

1. Amplifying and rectifying means comprising, in combination; anelectric valve having an anode, a cathode and a control electrode; meansapplying an alternating potential between said cathode and con-trolelectrode, means applying a unidirectional potential between said anodeand cathode, a transformer having a primary winding connected in seriescircuit relation with said electric valve and a secondary winding,rectifying means including a cathode connected for energization acrosssaid secondary Winding and having a pair of terminals between which aunidirectional potential appears, and a potentiometer connected forenergization across the first mentioned unidirectional potential andhaving a tap connected to the cathode of said rectifying means.

2. Amplifying and rectifying means comprising, in combination; anelectric valve having an anode, a cathode and a control electrode; meansapplying an alternating potential between said cathode and controlelectrode, means applying a unidirectional potential between said anodeand cathode, a transformer having a primary winding connected betweensaid anode and one terminal of said unidirectional potential applyingmeans and a secondary winding, rectifying means including a cathodeconnected for cnergization across said secondary winding and having apair of terminals between which a unidirectional potential appears, anda potentiometer connected for energization across the first mentionedunidirectional potential and having a tap connected to the cathode ofsaid rectifying means.

3. Amplifying and rectifying means comprising, in combination; anelectric valve having an anode, a cathode and a control electrode; meansapplying an alternating potential between said cathode and controlelectrode, means applying a unidirectional potential between saidReferences Cited in the file of this patent UNITED STATES PATENTS2,232,856 Idle Feb. 25, 1941 2,492,901 Sweet Dec. 27, 1949 2,594,769Hales Apr. 29, 1952 2,872,512 Massman et al Feb. 3, 1959 FOREIGN PATENTS416,705 Great Britain Sept. 19, 1934 OTHER REFERENCES Reich, Robert J.:Theory and Applications of Electron Tubes, McGraw-Hill, 1944.

